texts: Solar Eclipses for dummies: Step 1 - moon equatorial orbit around a planet without axial tilt

texts:
Note 1: I've studied downvoted questions and decided that I either asked too many questions or I sound like I'm setting a fantasy world. So I'm editing my question accordingly.

Note 2: I'm a language teacher. I learnt equations with variables but that was over 20 years ago and I remember little of it; I never learnt trigonometry and other more advanced maths, that's a fact, but if there's no way around it I'll do my best to tackle it.

Note 3: My approach to understanding eclipses, due to the above stated handicap, is removing all the complicating factors (namely, the axial tilt and the moon's 'ondulating' orbit). I assume that, if I can fully understand such a simplistic scenario, I can then follow the mechanics of the real Earth scenario.

Therefore, I have written below the points I am confident are true. The ones I don't know are asked as questions (Q) and formatted in bold.

Every new moon would be a total solar eclipse.
The path of totality would always cover the same area: a 250km  wide corridor with its centre at the equator (so 125km over the northern hemisphere and 125km over the southern hemisphere).
I think the path of totality wouldn't always cover the same area, e.g. always over Africa, so Q1: Is there a simple formula to predict which areas would be in the path of totality?
In real life, the moment of totality can vary from seconds to seven minutes. But in my study example, Q2: the period of totality should always be the same, right? Because the crossing path of moon and sun is always the same (while in real life the Moon can overlap the Sun at different angles and going in different directions)
Q3: How can I calculate this period of time?
What about the latitudes for whom the solar eclipse would only be seen as partial? I understand that the nearest to the path of totality, the more covered the sun will be, and vice-versa. Q4: Is there a set value that says e.g. for each km, another degree is visible?

If this question is still not ideally adjusted, please leave a comment so I can further improve it.


texts: statistical techniques for estimating distribution of mass

texts: I occasionally hear claims along the line of ' the mass of the universe is not uniformly distributed but actually is concentrated along a '  line, or some other lower  dimensional manifold & I would like like to know what statistical techniques, if any,  are used to make support these claims.  I'm not interested  in whether the claims have held, just in the what was used for the original analysis.  I have data  whose dimension I would like to estimate, and am familiar with correlation dimension.


texts: How bright would it be on the "face" of Titan

texts:
If you were planing a maned mission to Titan and wanted to find a landing site that would get the most visible light for the longest amount of time, your first logical choice would be the dark side of the moon since it faces the sun for a longer duration than the face would. ("face" and "dark side" corresponding to the colloquial definitions they have when referring to our moon) Also, unlike the on the face, you wouldn't have to worry about Saturn eclipsing the sun. This would put you in a range of brightness roughly equivalent of twilight on Earth due to the distance of the sun and the thick atmosphere of Titan.

But how bright would Saturn be when reflected on the face of Titan? Would it be bright enough to see anything if you wanted to go there, or would you need flashlights and night vision goggles?


texts: What is beyond the edge of the observable universe? Scientists say that the Big Bang is the cause of all creation in the known universe, but it would seem the bang must have happened in the center of the universe ?


texts: How can artificial gravity hold the water in swimming pool?

texts:
I was watching Passengers (2016). In this movie, a swimming pool exists in the space station. In middle of the movie, Artificial Gravity is turned off and the water rises, with the swimmer suffocating as they try to get out of the water.

Suddenly Artificial Gravity turned itself on again and the swimmer survives.

A clip of this scene is found on YouTube.

However, water is an anti-ferromagnetic material - it can't attract to magnetic bodies.

How then, can artificial gravity hold the water in swimming pool?

My question is totally different from this question.


texts:
I've seen a lot of beautiful pictures of the Milky Way from Earth such as this:

...but I can't understand what the cloudy ribbon at the bottom the horizon is. Is it a super-large nebula? Or is it due to the Gegenschein? What happens in the ribbon?


texts: Rotating azimuth/altitude to a focal point?

texts:
This is really a math question, but it's for use in astronomy, so:

Because reasons, I'm writing my own sky-viewing code.  I've found a few references for converting right ascension and declination to local azimuth and altitude; so far, so good, now I need to plot that coordinate in 2D.

It's trivial to turn az/alt into an azimuthal equidistant projection; just map azimuth to $\theta$ and altitude to $r$ where +90° is zero and -90° is 2.  However, what I really want is an azimuthal equidistant projection where the center is at a point of my choosing — for example, NW toward the horizon — ideally specified using two angles, $\theta$ and $\phi$.  With no modifications, az/alt is using a focal point directly overhead — how do I rotate that to my point?  (Continuing the example, I'd be rotating by $\theta$ 45°, $\phi$ 90°.)  I believe this is a spherical trigonometry question, but I'm having trouble grokking the references I've found well enough to do what I want.  Any guidance?


texts: Why do default coordinates from IR-optical observatories are usually not trustworthy, while from radio interferometers they usually are?

texts:
I have noticed in my experience that the coordinate solution within the headers of default reduced images from radio interferometers are commonly trustworthy to the arcsecond or less. From IR and optical observatories it is never so simple: the header solution from the default images is at most useful as a very rough guidance, off by an arcminute or more. Sometimes there is no useful header whatsoever, and the user needs to compare with, e.g., DSS of 2MASS to get good coordinates for her images, if she cares about that at all.

This has other consequences which in my opinion affect the idiosyncrasy of optical and radio astronomers, for example:

No coordinates in published figures is much more common within the optical-IR community than in the radio community
Finding charts. Radio astronomers do not know what are they, because they are not needed for radio observations.

Radio telescopes (this depends on the frequency also) sometimes require doing pointing calibrations during the observations. But in optical telescopes they also often require a guiding star, whose coordinates I imagine are properly tabulated. Regardless, the delivered images do not end up with a proper header.


texts:
I'm not sure if this is more a question for a 3D graphics forum, but I'm trying here first in case the answer has more to do with astronomy than 3D.

I am creating a model of the Earth and Moon in a piece of 3D software. To avoid the enormous scale of using real-world sizes, I am using a 1000:1 scale ratio.

These are the dimensions I'm using:

Earth radius = 6,371 m
Moon radius = 1,737 m
Distance from Earth to
Moon = 384,400 m

Since I have scaled everything equally, I would assume that the proportions of things would look accurate, but the moon looks very small indeed.

Here is a quick render from a camera placed just above the surface of the Earth, looking out at the moon:

The camera's focal length is 24mm, which I understand to be relatively similar to the human eye. I was expecting the moon to look similar in size to how it looks when you look up at it in real life but, as you can see, it's a tiny little dot.

Is there something obvious I'm missing here, or some explanation for this discrepancy?


texts: What is the minimum information I need to be able to draw the shape of an orbit of a body that orbits the sun? With this information how can I figure out the shape of its orbit?


texts: What is the actual resolution of Event Horizon Telescope?

texts:
I am quite impressed with the recently published image of M87* black hole. It appears that this image achieves spatial resolution well above and beyond what was available until today. But how high this resolution is, exactly?

The article "First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole" states that Event Horizon Telescope has theoretical diffraction-limit resolution of ~25 μas.

Another wiki article states that M87* has Swartzschild radius of 5.9×10-4 parsecs. Combined with the distance of 16.4 million parsecs, this gives me angular size of 14.8 microarceconds.

Even with the shadow of the black hole being 2.5 bigger that its radius, the resolution of a widely distributed picture seems to be much higher than 25 microarcseconds stated above. Is the image actually blown up well beyond its original resolution (i.e. becoming more a less an "artistic impression"), or Event Horizon Telescope is actually capable of higher resolutions (10 microarcseconds or less)?


texts: Pulsars with accreting disk in binary system

texts:
Following this line, I am wondering about the following question.

Accreting pulsars in binary systems are usually thought to accrete from a prograde disk, so increasing their spin in the process.

But why is the disk supposed to be prograde?


texts: Whats the time dilation difference between the earths reference and (near) the milky way galaxy central black hole?

texts:
How much difference in time is there between our time of reference and very near the black hole at the center of our galaxy.

I was trying to get answer in terms of something like "1 year in here equal to 1 day at near some black hole".

As the gravity slow down the time, means all the activities are slowed down i.e even nuclear reactions would slow down (when looking from our time of reference). The question can be put like how much slow it is there compared to our time frame ?


texts: How do I create a galaxy stellar mass function?

texts:
Suppose that I have an array of stellar masses of tens of thousands of galaxies, and that I also already know what the total "survey volume" is (in Mpc^3) within which all of those galaxies are contained. For context, my data is from a simulation of galaxy formation at redshift ~ 0, rather than from an observational simple -- so in principle I don't think I need to worry about incompleteness corrections at the faint (low-mass) end.

Given my array of stellar masses and the total survey volume in Mpc^3, how do I create and plot the "galaxy stellar mass function" that I always see people talking about? Isn't it just basically a histogram of the stellar mass array, and then divide the # of galaxies in every bin by the survey volume (it's almost just like a normalization constant)?

(Of course this question could equally apply to galaxy luminosity functions.)


texts: Does Ceres have an exosphere similar to the Moon?

texts: Thinking about the question and answers for Does the Moon have any oxygen in its atmosphere? begs the question, despite being considerably smaller than the Moon and further away from the sun, does Ceres have a similar atmosphere as the Moon?


texts: Should only spherical satellites be considered 'moons'?

texts:
Since Titan and Ganymede fall into the same category as Deimos and Phobos or the components of planetary rings, the category of moons, it's like if all asteroids were considered planets. Tiny irregular satellites are called 'moonlets' but still fall into the category of moons.

Is there any distinction between the natural satellites and should there be one? From my point of view, only equilibrium-shaped spherical moons should be considered moons. While natural satellites are all satellites, the spherical ones should be moons. Otherwise it would be extremely weird that Deimos and Phobos fall into the same category as our Moon or the Galilean Moons. For example, Pluto should be considered having five natural satellites, and one of them (Charon) is a moon.


texts: How can many stars be formed from the remains of one supernova?

texts:
A supernova is the explosion of a single star; so how is it that thousands of stars can "be born of" that one explosion (presumably only using the unspent fuel / lighter elements of the original)? Does that also mean the stars coming from a supernova cannot possibly become supernovae themselves?
For example, according to Wikipedia, the Rosetta Nebula has about 2500 including a couple of O-type stars!

approximately 2500 young stars lie in this star-forming complex, including the massive O-type stars HD 46223 and HD 46150

Edit to reduce confusion and risk of reinforcing my false premised path of questioning: I somehow had the idea that nebulae came from single supernova explosions and that all nebulae were planetary nebulae. After research, that was an absurd understanding on multiple levels.


texts: Companion Sun the cause of comet impacts with Earth

texts: On television, I heard a scientist who believes that our Sun has a companion (brown dwarf) Sun, that is responsible for comets destroying life here on Earth every 26 million years. He proposed the theory that when this companion Sun travels through the Ort Cloud, every 26 million years, it brings billions of Comets with it into our Solar System and inevitably one crashes into the Earth. Any thoughts on this?


texts: How much mass does our sun need for exploding like supernova?

texts: Beside that, is that possible our sun became pulsar? And if not (and i know likely) but how much more mass does it need to become one ?


texts: Relativistic Mercury orbit around the Sun

texts: My question is the following,would the scalar of precession of Mercury orbit be the same if Mercury orbited Sun in the oposit direction?


texts: How to the find radius of a galaxy given its inclination?

texts: If the semi major and semi minor axis of a galaxy are 3" and 1" respectively, how would you find the radius of the galaxy?


texts: finding Dec and R.A of a star by having Dec and R.A of another star

texts:
How can we find Dec and R.A of a star by having Dec and R.A of another star.

For example in the following picture , we have that for Errai (Dec: 77 , R.A 23H 40M). How can we find Dec and R.A of Gamma Delphinus. Note that we can't use Polaris for example because of cloud or something else. I want answer for when we have telescope and when we don't have telescope.


texts: Help understanding this unsettling image of Titan, Epimetheus, and Saturn's rings?

texts:
The NY Times article Saturn’s Rings Are Sculpted by a Crew of Mini-Moons is really interesting and links to the recent paywalled paper in Science Close Cassini flybys of Saturn’s ring moons Pan, Daphnis, Atlas, Pandora, and Epimetheus

But I absolutely can't understand one of the photos in the NY Times article, shown below. Titan seems to be...

behind Saturn's rings, and yet it is
huge relative the spacing of the rings, and yet it
appears to be out of focus while the rings and Epimetheus are in focus.

Can someone help me understand how all of these can be true at the same time?

  In the foreground, the moon Epimetheus appearing to hover above Saturn's rings. Epimetheus is dwarfed by Titan in the background.CreditNASA/JPL/Space Science Institute


texts: Are the terms "PG 1159 star" and "pre-white dwarf" synonymous?

texts: Are the terms "pre-white dwarf" (as in Gies et al. 2020, "Spectroscopic Detection of the Pre-White Dwarf Companion of Regulus") and "PG 1159 star" (as described, e.g. in Werner et al., 1996, named after the prototype object PG 1159-035) synonymous? I'm not entirely sure whether there are any pre-white dwarfs that are not PG 1159 stars, nor if there are any PG 1159 stars which are not pre-white dwarfs.


texts: Accurate way to programmatically generate a main sequence star?

texts:
I am working on a (personal) programming project, part of which involves generating random stars and their parameters.

In order to create a procedurally generated star, I want to randomly select as few parameter values as possible, and then extrapolate the rest using formulas.

For instance by interpreting the Stefan-Boltzmann law I can derive the star's luminosity based on the surface temperature and the star's radius:

$$
L = 4 \pi R^2 \sigma T_{e}^4
$$

There are however other parameters that I would like to generate, such as the mass of the star. What seems to be able to help me is the mass-luminosity relation:

$$
\frac{L}{L_{\odot}} = \left(\frac{M}{M_{\odot}}\right)^a
$$

By knowing $a$ (based on my randomly selected mass) it seems that I can derive the star's luminosity. By glancing at the Hertzsprung–Russell diagram (e.g. this one) I can see that I can perhaps somehow calculate the radius of the star, but I'm not entirely sure how.

There is an existing star "generator" which can be found here, however this one interpolates existing data using logarithms.

My full question would be, is there a way to "generate" a "regular", main sequence star, starting from one or two parameters and extrapolating the rest using formulas? Is there a sensible relation between the mass of the star and its radius that can be used to generate a "realistic" star? Or would most parameters need to be interpolated from existing data?


texts: How does inflation explain why the curvature in the early universe was flattened out and now results in a flat universe?


texts: How does the Grand Tack Hypothesis explain how Jupiter formed inside the frost line?

texts:
The Grand Tack Hypothesis states that Jupiter formed at roughly 3.5 AU from the Sun, then interacted with a large portion of objects in the Solar System before settling into its current orbit.

Yet as I found from researching for an answer to this question, giant planets generally form beyond the frost line - in fact, this explains why the giant planets are cut off from the terrestrial planets.

How does the Grand Tack Hypothesis get around this?


texts: How long would it take to reach the edge of the reachable universe?

texts:
How long would it take to reach the current edge of the reachable portion of the universe, with the following bounds in mind:

We figure out a way build a space ship to provide a constant 1 G acceleration for an extended period of time.
We accelerate until we are halfway there, then decelerate past this point (so we stop when we get there.
Our target is about 15 billion lightyears away.  As per http://curious.astro.cornell.edu/about-us/104-the-universe/cosmology-and-the-big-bang/expansion-of-the-universe/616-is-the-universe-expanding-faster-than-the-speed-of-light-intermediate galaxies past 4,740 megaparsecs are no longer reachable. Using this site http://www.convertunits.com/from/megaparsecs/to/light+years to convert megaparsecs to lightyears means this "unreachable" point is currently 15,459,812,396.5002 lightyears away.  Let's simplify to 15 billion lightyears, which is still supposed to be reachable.
We somehow work out all the details of life support, collision with particles at relativistic speeds, etc...

I would like to know the time the traveler experiences, and the time that everyone else (e.g. those on earth) experience.


texts: What would this moving point of light be?

texts:
Tonight (10:00 PM EST Middlesex County, Mass.) when looking at a mostly clear sky I observed what I at first believed was a meteor. This point of light was moving east to northeast, and that would be in the vicinity of the Lyrid meteor shower.

In the app Star Walk for iOS it says that the "n-Lyrids" meteor shower peaks on May 9th. However, information I found online about this meteor shower says it already peaked back in April. (I did see a bright meteor a couple weeks ago.)

Can anyone offer insight on possible meteors right now? I highly doubt that this was a meteor though, because it lasted way too long, probably two minutes.

My next guess was the International Space Station but NASA's Spot The Station did not show any viewing times for my area today. The Star Walk app also showed the ISS well below the horizon.

This leads me to conclude the object was a plane, however there were no blinking lights and the only time its light changed was when it passed behind a thin cloud.

It could also have been a satellite glint such as an Iridium flare. I did not see the beginning of the light's appearance, so it is possible I missed the flare. However flares do not last for minutes, but glint from solar panels or other satellites may last this long.

What did I see?


texts: I sometimes hear about astronomers using an arc spectrum to calibrate observations. For example a "He-Ar arc spectrum". What is an "arc" in this context? I assume it's nothing got to do with angles (arcmin, arcsec, etc.).


texts: From our world's perspective, does the full moon look larger in one city than it does in another?

texts:
When I was a very little girl, my dad talked about the HUGE full moon he saw while in the navy. He made the comment during a full moon we were having in Western NYS. He said, this (harvest) moon is nothing compared to the one he saw.

Now years later, I was with my grown son, who's a geologist and who has been all over the world but not during a full moon. He told me my dad was wrong. My son said that the full moon is always about the size of a penny when you hold the penny up to compare the size of the moon to it.

But I have seen pictures of HUGE full moons over cities my whole life and I assumed my dad was correct. Is there a place where I can travel to see a HUGE full moon that would be much bigger than the full moon I see from the shores of Lake Erie? I understand that the horizon makes the moon bigger but the pictures I have seen were not moons on the horizon.

I've searched Stacker's data base but I didn't see this question.


texts: How do I prevent or reduce shake when observing with binoculars?

texts:
I have some 16 x 50 binoculars that my parents bought me years ago. Recently I have tried to do some basic lunar and planetary observations with them but I am seriously struggling with shaking. This was most noticeable tonight while attempting to observe the ISS.

While I accept that keeping the image of a moving target stable is going to be next to impossible, I would like to know how I could reduce my shaking while observing the moon and other objects.

Is anyone able to provide some simple techniques to reduce shaking?


texts: What does oxygen on comet 67P/Churyumov-Gerasimenko mean?

texts: Recently, the Rosetta mission found oxygen on the comet 67P/Churyumov-Gerasimenko. According to theories, oxygen should not be in the state in which it is on the comet. What are the previous theories that didn't support this, and what is the explanation for the oxygen-rich environment? How will this change our understanding of the formation of the Solar System?


texts: How come the Sun does not make the Moon crash on the Earth?

texts:
As the Moon loops around the Earth, on one side of the Earth it moves toward the Sun (let's call it downward side) and on the other side it moves away from the Sun (let's call it the upward side).

Now, I imagine the Sun's gravity attraction accelerate the Moon on the downward side and slows it on the upward side. This should raise the Moon's apoapsis on the upward side and lowers its periapsis on the downward side, gradually putting the Moon on a collision course with Earth.

Yet, this does not happen. I am curious to understand why. I suppose even a very very slim effect should build up upon billions of years, so is there a fault in my reasoning or some tidal effect correcting the Moon's trajectory?


texts: Mass, Radius, Colour, Size, Type of a Star from the Hipparcos Catalog

texts:
Using data from the Hipparcos Catalog download file, is there a way to determine the Visual or Apparent Magnitude from the data within?

Can I obtain the Mass, Radius, colour, temperature, type (dwarf, sun-like, hypergiant, etc) of the star from the catalog?  Which column relates to which item i'm looking for?  Any examples?


texts: Why does the Sun's surface contain lithium?

texts:
As far as I was aware, stars don't usually have lithium, but it has been observed that there is plenty of lithium on our star's surface.

In addition, a team lead by Garik Israelian took a census of 500 stars, 70 of which are known to host planets and about a quarter of which are particularly Sun-like. Using ESO’s HARPS spectrograph, this team of astronomers (see here) found that the Sun-like stars which host planets have destroyed their lithium much more efficiently than “planet-free” stars.

Why do Sun-like stars have lithium on their surfaces and why do stars that host planets destroy their lithium more efficiently?


texts:
This answer to Why don't or (can't) stars be more than 325 or so times the mass of the sun? What limits their size? includes the following:

...The upper limit you refer to is for compositions similar to the Sun. For stars born in the distant past that were metal-poor, or even born from primordial material with no metals, the upper limit could be much higher.

Question: What was the absolute limit to the possible sizes of the first stars formed from "primordial material with no metals"? I'm primarily asking about the size that was possible to exist as a star. There may be other limits associated with the possibility of formation in the first place due to matter distribution and that would be interesting to know as well.
NOTE: There is also the well-received and as yet unanswered question Formation of the First Stars If this topic is better addressed as an answer there instead, then please do so and we can close this as a duplicate.


texts: Difference in energy released in stellar mass black hole merger and supermassive black hole merger

texts:
Super massive black holes are usually millions of times more massive than stellar mass black holes. I have read on SE and over internet that 3M☉ worth of energy is released in black hole mergers (not sure which type of merger). I have tow related questions:

What is the difference in energy released from a stellar mass black hole merger vs. a supermassive black hole merger?
How much energy will be released in the super massive black hole merger when Milky way and Andromeda will merge in few billion years?


texts: Ladakh India where the moon (Ramadan moon) is sighted but not in rest of India

texts: Today 22 May 2020 around 3 p.m Ladakh India sighted new moon(Ramadan moon) but not in rest of India.I read many articles acc. To them it is not visible today, then how it was seen from Ladakh... .


texts: Efficiently calculating power spectra from galaxy catalogs

texts:
I am dealing with a problem which requires calculating either the correlation function or the power spectrum. At times, the 2-point-correlator seems the better route, at others, the PS. Right now I am having some questions about how to practically calculate a PS.

Here is the basic setup: I have a mock galaxy catalog. Let's say I want the PS. I could Fourier transform the 2PC, but let's say I want to avoid working with a 2PC code. So instead, I make the assumption that the galaxies trace the density field (it helps that I have the DM halo masses from the underlying simulation which produced the mock).

I bin the galaxy catalog, giving me a coarse-grained list of masses for each bin, $\{m_{ijk}\}$. It is trivial to turn this into a density contrast list $\{\delta_{ijk}\}$.

There are a couple of options now to proceed to calculating the PS. Formally, the PS is given by
$$
P(k) \sim \langle \, |\tilde \delta(\vec{k})|^2 \,\rangle
$$

up to some normalization, with $\tilde \delta$ being the fourier transform of $\delta(\vec{x})$, the full density contrast field, and the angle brackets denoting volume averaging. The seemingly natural thing to do would then be

FFT my binned list $\{\delta_{ijk}\}$
get list of values $\{ P_{ijk} \}$
average this list to get the PS $\{ P_k \}$, now just a function of $k$ instead of $k$-space position.

This is potentially problematic for me, as unless I bin over large scales, the memory required to store the zeros present in the array of binned values is too large. With the data I have, binning at $
\sim 10$ Mpc$/h$ spaces or greater is needed to get a managable array.

My solution for calculating the 2PC was to avoid calculating an array entirely, and instead performing a regrouping operation to bin the catalog. This keeps the memory usage proportional to the catalog length instead of to the binning resolution cubed. However, it effectively means I am dealing with a sparse density array, which AFAIK cannot be used directly in most existing FFT codes.

This leaves me with a dilemma. I can either coarse-grain my density array $\{ \delta_{ijk} \}$ even more, losing information at $\sim 1$ Mpc scales, or else I suppose I could interpolate the density, giving me a full function $\delta(\vec{x})$ that I could pass some coarser mesh into, and then pass into an FFT. The problem with interpolating is that this operation requires the (now implicit) knowledge of the empty cells in the sparse array.

On the other hand, one SO post has a comment suggesting to merely calculate the Fourier integral instead of using FFT methods. I fear this would still present a problem, as this takes the time complexity from $O(n\log(n))$ to $O(n^2)$, and $n$ for me is $\sim 10^6$ or higher (becoming as high as $10^8$).

Am I missing something? I feel like people calculate PS and 2PC's all the time for catalogs this large, and like my attempts at solving this issue could be flawed. My precise question is, are my options just as I have laid out, or is there another way of handling this calculation I have not described?


texts: What is the acceleration of the stars' speed in the Universe? Positive or negative?

texts: I have read quite different opinions about that, so can someone tell me what is the sign of the acceleration of the stars in the Universe if we accept that the center of the Universe is the beginning of the coordinate system? At least what is considered as correct finally :)


texts: What are the large round dark "holes" in this NASA Hubble image of the Crab Nebula?

texts: I came across this image of the Crab Nebula taken from NASA Hubble telescope. What are the large round "holes" and how are they formed?


texts: Modeling planet rotations (time of day, obliqueness, etc.)

texts:
I created this solar system model using POV-Ray:

by following these instructions:

https://ssd.jpl.nasa.gov/txt/aprx_pos_planets.pdf

The next thing I want to do is orient/rotate each globe correctly according to the time of day, time of year, obliqueness, position in its orbit, etc. but cannot find any instructions on the JPL website. How can I go about completing this task? Thanks.

Part Two

[deleted]

Part Three

So, α (right ascension), δ (declination) and W are Euler rotation angles. But what are the starting conditions before applying these rotations? Should the North Pole of the planet be aligned with the z-axis? Should the plane formed by the prime meridian be perpendicular to the y-axis?

Also, which axes do I rotate around, and in what order? I am guessing δ should be rotated first around the y-axis, then α around the z-axis. But W also looks like it should go around the z-axis. I am confused.

Part Four

I found another PDF document which on page 27 gives an equation for δ, α and W. (Not sure how to reproduce it here.)

https://depositonce.tu-berlin.de/bitstream/11303/6237/4/burmeister_steffi.pdf

I think that according to that PDF file I need to rotate around the z-axis by W, around the x-axis by (90-δ), and around the z-axis again by (90+α), in that order. Lastly, an additional rotation (around the x-axis?) by 23.43928 degrees must be done to get the body out of the ICRF frame and into the ecliptic frame.

But I still don't know the starting conditions. I.e. before applying the transformations, should the globe's North Pole point upward? Should the intersection of the Prime Meridian and Equator lie along the x-axis? Or, am I totally wrong, and should I perform the inverse matrix calculations instead? So far I have not gotten results that match what I see in Celestia for the same Julian Date.

Part Five

In some instances I am able to get "close" results using the above method. In others not. For instance, Mars, Saturn, Uranus and Neptune are "close" to correct. (At least, the poles - the blue arrows - are pointing in the same directions.) The Earth is not.

The correct results are the ones in the larger Celestia program window. My current POV-Ray results are in the smaller window to the left. The dark arrows indicate the parent (ecliptic) reference frame. The bright arrows indicate the body reference frame. The view in all images is from the top down on to the ecliptic plane.


texts: How do I find the RA of sunset and sunrise in a specific location?

texts: I want to make some observations with a telescope in Hawaii on Mauna Kea but I am living somewhere else (not Hawaii) and I want to plan a night's viewing on the Hawaiian telescope. How do I find the RA range of the night? In other words; how do I find the RA range of the first object observable to the latest object observable for a particular time (of year) for a specific location (in this case Hawaii)?


texts: Why does the Earth have a z-component at the start of the J2000 epoch?

texts:
When I go to the NASA HORIZONS webpage

https://ssd.jpl.nasa.gov/horizons.cgi

and ask for the VECTOR coordinates of the Earth on 1 January 2000, it tells me that Earth has the following coordinates in the J2000 epoch:

X =-1.756637922977122E-01 Y = 9.659912850526895E-01 Z = 2.020629118443605E-04

These are measured in astronomical units. Quoting from the webpage:

Reference epoch: J2000.0

XY-plane: plane of the Earth's orbit at the reference epoch

X-axis  : out along ascending node of instantaneous plane of the Earth's             orbit and the Earth's mean equator at the reference epoch

Z-axis  : perpendicular to the xy-plane in the directional (+ or -) sense              of Earth's north pole at the reference epoch.

But these figures don't make sense! The z value should be EXACTLY zero, since we are measuring at 1 January 2000. Also the x should be exactly 1, and the y should be zero.

What is going on?


texts: I already googled a face-on galaxy and an edge-on galaxy, but I couldn't find any proper information. Would you explain them to me?


texts:
The speed of light is the upper limit at which conventional matter can travel. However, jet streams propel "material (...) at a significant fraction of the speed of light" (Wikipedia).

Let me rephrase the question, as I have made a mistake. Do we know what exactly emits the black hole in a jet stream?

And if they emit something than they put this matter back into this universe, which will then again serve as potential matter they could suck in.


texts: Stellar Classification Table and Star RNG

texts:
I found a table that was based on data from 2003 for Stellar Classification, and I can't get to the given data source. I plan on using the table as a basis for a program that spits out random star systems with stars +-5% of the given data.

I know type R was renamed to C so I am already throwing that out. Is there anything else I should ignore from this table or add?

Or this table is crap and should not be used as there are glaring errors.


texts: Can I derive the position of my house's shadow from sun altitude?

texts:
I'd like to pull in my awning if my house's shadow has reached a point where the awning has no use any more. The house is almost perfectly aligned in a North-South direction, the garden with the awning is in the east.

My home automation (fhem) offers a module that gives me a variety of astronomic parameters, based on my location and altitude:

 "SunAlt": -3.3,
  "SunAz": 309.5,
  "SunDec": 22.3,
  "SunDiameter": 31.5,
  "SunDistance": 151752013,
  "SunDistanceObserver": 151752409,
  "SunHrsInvisible": "08:10",
  "SunHrsVisible": "15:49",
  "SunLon": 72.7,
  "SunRa": "04:47",
  "SunRise": "05:16",
  "SunSet": "21:05",
  "SunSign": "Zwillinge",
  "SunSignN": 2,
  "SunTransit": "13:10",

Is it enough to target sun's altitude above the horizon? I would think so, but I'm not sure... Currently I'd withdraw the awning when sun's altitude goes below 54⁰.

Edit:
Sorry, I seem to have written my question in a very unclear way. Here's more information:

I know my location, at least with GPS precision. Given that location, fhem's astro module gives me all kind of information about sun, moon,...

I have a patio that's to the east of my N-S aligned house. The house is a row house, so for my purpose it's long enough that only the roof is interesting for the shadow.

Sun shines onto the patio in the morning until (currently) something like 15:00. I tend to make shadow with the awning in the morning. After 15:00, the patio is in the shadow of the house and I don't need the awning any more and I would like to remove the awning automatically.

I looked at fhem's astro module exactly at the time when the shadow was far enough on the patio that I could remove the awning. I took the "Sun altitude" value (54⁰) and now the awning is removed when the sun reaches an altitude of 54⁰

This was some days ago and I think this might not be good enough: it seems as if the shadow is extending more and more until the awning is removed. Or the other way round: It seems that I have to adjust the 54⁰ to, maybe, 50⁰ now to get the right timing.


texts: Why does the angular size of the Moon change?

texts:
I know that the orbit of the moon is elliptical.
But I cannot understand this graph:

The number of 'bumps' in the graph is around 13~14 in a year, so I concluded that the each 'bump' indicates one lunar month.
But why aren't these bumps symmetrical? Since the moon revolves around the Earth once in one lunar month, shouldn't they be symmetrical?


texts: What is the boundary in the atmosphere seen in this video?

texts: This video, which shows time-lapse views of Earth from the ISS, consistently shows some sort of hard boundary in the atmosphere, below which there seems to be significant reflection from sunlight and/or Earth's cities and above which there seems to be nothing impeding the view of black space.  What is this boundary?  I don't think its the edge of the atmosphere, partly because the atmosphere has no hard edge and partly because the aurorae (an atmospheric phenomenon) seen in the video exist, at least in part, above this boundary.


texts: How do you find the positions of celestial objects in the sky?

texts:
I want to write a program which, when given a date, a time, latitude and longitude, returns a list of the planets, Messier objects and NCC catalogue objects what are visible in the sky at that time and place?

Are there any APIs which can do this or would I have to calculate the positions?

Preferably, this should be accessible using JavaScript


texts: How many photons does it take to determine the existence of a distant object?

texts:
This applies to any object, but I see the recent discovery of the oldest, most distant galaxy and it started me wondering what the limits are. Presumably you can do better with a bigger telescope and longer exposure, but I'm curious about literally how many photons you need to collect to decide whether or not something is actually there. And then presumably you need a bunch more to determine its red-shift and angular size and rotation etc.
I have absolutely no feel for these numbers.  Is it tens of photons or a millions of photons?


texts: Are there currently observed systems of close (narrow) binary brown dwarfs?

texts:
All over the Universe, there are (gravitationally bound) binary star systems. Considering the huge number of brown dwarfs, are there currently known double systems of gravitationally bound binary brown dwarfs? Given their comparatively low gravitation, how long would they need to melt together to a larger object?
What happens if binary brown dwarfs collide? Is this anyway a matter of any interest?


texts: Is it possible to mount a telescope on a plane? Is it beneficial?

texts:
I was wondering if any planes had mounted telescopes with the intent to observe the stars. I understand that the atmosphere itself can warp and hinder incoming light and even completely obscure views on cloudy days. Would it be possible to have a telescope which could account for the speed of the airplane and remove motion blur? Would it even be worth it, seeing as the size of the lens would also be limited? Could we see anything interesting that a terrestrial scope of the same size would miss?

Hobbes has mentioned SOFIA as a great example of this being done. Does anyone have more information on the benefits of a plane mounted telescope over one on the ground for noninfrared observation?


texts: Why does earth's north pole roughly point in the same direction throughout the year?

texts: I know there is a gioscopic explanation but I was under the impression that Earth is traveling in a straight line through space that has been curved by our sun's gravity ,so my question is why doesn't one hemisphere always point away from the sun ? It just seems like a bit of a contradiction that gravity can curve the fabric of space but has no effect on earth's axis...


texts: Calculating and mapping the best visibility of celestial occurrence

texts:
Recently I found a fantastic website in-the-sky.org, from here we can simply pick up any astronomical event and check its visibility in any part of the Globe.
For occultations, for example, we have very nice maps like this below:

There are a lot of conjunctions, occultations, eclipses, and so on described fairly in detail. I think it's the best website so far for people making Astro calendars.
The problem is, that if I checked some conjunction i.e. Mercury with Mars on August 19, 2021  I spent quite a lot of time checking which located around the Globe is the best for watching this event. I took into consideration the solar depression, not lower than 6 degrees (end of civil twilight), and an altitude of these 2 bodies above the horizon (not lower than 3 degrees due to atmospheric extinction). Finally, my hand-sketched maps are looking like this:

plotted in the Day & Night Map at timeanddate.com

sketch plotted in Google Maps

Circumstances checked with stellarium-web.org
So basically is quite a lot of work by checking which location is the most appropriate to watch the moment of conjunction ideally (I mean the moment of biggest approach these 2 planets, which lasts maybe...30mins or so). Concluding I would like to ask about the possibility of auto calculate stuff like this. If for example, I would put in one column the min solar depression, in another column the min altitude of these planets, some tool would bring me the map as presented above?
Is it possible i.e. with Python or other (I am only basic with soft)?
Or do you know web services, which do the calculation such as this for you?
I fund some query here:
How to calculate conjunctions of 2 planets
but it applies to calculate the dates and geometrical circumstances of the conjunctions. I would like to have something in the map as presented above.


texts: How can we see stars if they are hundred years of light far from the Earth?

texts: So the right question is, is the light years counted from that second when you look up to the sky? If that so, how can we see the stars from the telescope (which I think it starts when you put your eyes on it, same as when you look up to the sky), that they say it's 5000 of light years from earth? If you say these lights are already started 5000 years of light ago, then there should be so many changes happened to these galaxies or stars in that timeline. Thus, for example, there should be no way to know, if an earth-like extrasolar planet is still earth-like.


texts: Orange light that rises quickly and moves of to the righ

texts: I have recently noticed an orange "star" (or what I presume to be a star), rise above the hill line behind my home. It rises later than every other star and rises within a few hours while the other stars are stationary! It moves off to the right when half way in the night sky this happens every night when clear for the past few months. I also believe I'm looking south. It's really bugging me. Could anyone identify this object from my description?


texts:
So the visible light from stars can be used to identify the elements in that star by looking at the spectral emission lines and comparing those lines to emission lines of various elements (and their isotopes) here on earth.  These well-known line wavelengths can also be used to determine the relative motion of that star to the earth by looking at the red (or blue) shift of wavelengths of those spectral lines.  It would then be reasonable to assume that our own sun emits those same well-defined spectral lines, which should show up at specific wavelengths (based on the elements in the sun).

However, sunlight appears (mostly) white, and using a prism shows a rather consistent rainbow of color across the visible spectrum, rather than what one would expect to see (based on analysis of emission spectrum from other stars) of spikes at specific wavelengths.  So, what is causing the full-spectrum light from the sun to appear at the surface of the earth if what I'm assuming is specific spectral lines being generated from fusion on the sun itself?

I'm sure I'm missing something in my understanding, but I'm not sure what it is.  I understand (from this question: How deep is the "A" Fraunhofer line in the solar spectrum? Is it from the Sun's or Earth's atmosphere?) that the earth's atmosphere absorbs specific wavelengths of light, but why would the sun's light be consistent across its visible spectrum if the typical star light is generated at specific spectrum wavelengths?


texts: What is the angle between the equator of the sun, and the plane of the Earth's orbit

texts:
I want to know the angle between the plane that passes through the centre of sun and is perpendicular to its spin axis, and the plane that contains the orbit of earth around sun?

Is this a fixed value or it is variable over time (and if so, how does it vary) !


texts: lunar calendar accuracy for predicting new moons

texts:
I wonder, how accurate the lunar calendar is?
Can we predict the new moons precisely for tens of years in future?
If we know all factors that affects the movement of the moon, then why it is not possible to predict it?


texts: Is it possible to use Hubble Telescope to observe Earth in the past?

texts: We can observe many astronomical objects and structures beyond our solar system,  however our observations are as the objects appeared in the past due to the speed of light. My question: "Is it possible to use Hubble Telescope to observe Earth as it was in the past" by turning Hubble's lens to a previous location of Earth in space?


texts: What irradiance does the Moon receive during a total lunar eclipse?

texts:
As we know, the total solar irradiance normally received by the Moon is about 1361 $W/m^2$ (the same as the top of the Earth's atmosphere). Of course, this changes during lunar eclipses, but the Moon doesn't go completely dark even during total eclipses (it's usually just a dim red). It still receives light through the Earth's atmosphere. My question is how much?

I've tried googling this, but all the search terms I could think of just gave me a bunch of unrelated astrology results. Surely people have measured this.

The worst case irradiance for any part of the Moon during a total eclipse is fine for my purposes, but I wouldn't mind a paper with an intensity curve over time if there are any.

Edit:
This is not a duplicate of "Red Moon a Characteristic of all Total Lunar Eclipses?" That question is asking if all lunar eclipses are red and/or if the amount of redness varies. I'm asking how much light hits the Moon (per second per area) during a total lunar eclipse. Furthermore, none of the answers there even mention irradiance.


texts: Would the (orbitting) speed of the Earth change if suddenly the sun disappear and the Earth is thrown into space?

texts:
Usually an orbit is considered as an acceleration. So if the Earth has a speed of about 100.000km/h around the sun.
Now I think there is some relativity involved, so from which point of view shall we observe those speeds? But lets imagine that we stand on mars which stays still compared to the Earth and the sun, only the Earth is moving.

Shall we measure a different speed when the Earth is thrown into space? Would it be more of less than 100.000km/h? Or is there something missing?


texts: How Wide Would the Habitable Zone Be in a Singular Red Giant System?

texts:
Astrobiologists looking for signs of life outside Earth usually take excitement over planets orbiting red giant stars because a larger, brighter star usually means a farther-away but still wider habitable zone, a slice of space where liquid water would be possible.

To put this in perspective, a single red giant can have a luminosity ranging anywhere between 1,000 and 10,000 times brighter than our sun.  Would that mean that a habitable zone in a solar system orbiting only one red giant would be 1,000 to 10,000 times as wide as our own?


texts: Is the nose of the solar system and the solar apex the same thing?

texts:
Results from the IBEX satellite indicate the nose of the solar system is pointing to the constellation Scorpius.  Various sources say the solar apex is pointing to the constellation Hercules.

Are the two different, or is simply the information about the location in conflict?


texts: Moon is a planet by "Clearing the neighborhood" condition?

texts:
Whether the Moon (Earth's natural satellite) is a planet is an old debate in planetary science.
Though I do not agree that Moon is a planet, I found something difficult to clearly understand.

According to the 2006 IAU definition of planet, a planet must satisfy Clearing the neighbourhood condition.
And some criteria for the condition are introduced in the Wikipedia article about Clearing the neighbourhood.

Stern–Levison's $\Lambda$

$$\Lambda = \frac {m^2}{a^{\frac 3 2}} k$$

Margot's $\Pi$

$$\Pi=\frac {m}{m^{\frac 5 2}a^{\frac 9 8}} k $$

In the above equations, $m$ is the mass of the body, $a$ is the body's semi-major axis, and other factors are described in the Wikipedia article. Both criteria are said to be satisfied if the calculated value is greater than 1.

My calculations are simple. Let $m_{Moon} = 0.0123 \times m_{Earth}$ and Moon's other factors (such as $a$, $k$ and $M$) have the same values as Earth's. Then I can get...

$$\Lambda_{Moon} = 0.0123^2 \times \Lambda_{Earth} = 23.147$$

$$\Pi_{Moon} = 0.0123 \times \Pi_{Earth} = 9.963$$

Both $\Lambda_{Moon}$ and $\Pi_{Moon}$ thus satisfy the Clearing the neighbourhood condition. Though I do not calculate the Soter's $\mu$, it will not change my results.

What is wrong with my calculations and results? Do I miss something about the condition and the criteria? Or is there something wrong with the Clearing the neighbourhood condition?

Edit in response to comments:

This question can be related to the idea that the Clearing the neighborhood condition is inadequate and ambiguous for the planet definition.
More deeply, this question can be related to the idea that 2006 IAU definition of planet is logically ambiguous and clumsy.
For example, the 2006 definition of planet defines the Moon as a satellite and not a planet.
If one celestial body can be defined as a planet or not without rules and conditions, why other conditions are needed? All we need is just a planet list, not other planet conditions.

And...

Frankly speaking, the Clearing the neighborhood condition is like comedy.
The condition says "Planet must sweep out other bodies" ...
Then says "Except satellites" ...
Then again says "Except bodies having no significant size" ...
Then again "Except bodies having resonant orbit" ...
Then again "It may take billions of years" ...
Then again "Sweep-out process and time are influenced by other planets and bodies, actually" .......

It is obvious that sometimes the Clearing the neighborhood theory is useful. But it is inappropriate for the rule and definition requiring strictness.


texts: Will the nebula of Betelgeuse be visible to the naked eye? How bright, how large, how soon, for how long?

texts:
When Betelgeuse goes core collapse supernova it will leave a supernova remnant. Will it become visible to the naked eye? If so, in what time frame will it be visible. Will it be star like from the beginning, or only after decades or centuries of expansion, to then fade away as it thins out?

The Crab Nebula seems to have had a progenitor of similar mass as Betelgeuse, also a core collapse supernova about 800 years ago, and is about ten times further away. Its supernova remnant seems to be about 300x400 arc seconds in size, so about a fifth of the Moon's diameter on the sky. But it is not visible to the naked eye.

If Betelgeuse's remnant becomes a pulsar, would light from its jets hitting gas be visible to the naked eye, and further out earlier than the supernova remnant itself?


texts: what determines the density of atmospheres

texts: What factors determine the atmospheric density on various planets and moons? Some larger bodies have less dense atmospheres, while some smaller ones have a more dense atmosphere.


texts: Are there any ALMA or JCMT detections of extraterrestrial phosphine that have been confirmed by direct sampling?

texts:
Please note that I am not a professional astronomer but an interested layman. I've informed myself on the matters below by perusing arXiv--there are likely other publicly-accessible primary sources I don't know about.
Like many people, I am excited by the possible detection of phosphine on Venus. The most rigorous counterpoint to this claim thus far is probably this paper re-analyzing the initial paper's data and arriving at a different conclusion. It occurred to me that there may be extant data from actual probes that can shed light on the latter's analysis. This leads to four questions, listed in order of usefulness:

Is there existing phosphine-related probe data from phosphine-producing gas giants (I've seen Jupiter directly mentioned) aligning or not aligning with Atacama Large Millimeter Array (ALMA) or James Clerk Maxwell Telescope (JCMT) observations?
Is there existing non-phosphine-related probe data from Venus aligning or not aligning with ALMA/JCMT observations?
Can these instruments make detections of phosphine in Earth's atmosphere, which could then easily be measured against physical sampling?
Is there existing non-phosphine-related probe data from extraterrestrial bodies aligning or not aligning with ALMA/JCMT observations when interpreted using the same statistical methods as the initial Venus phosphine paper listed above?

Any explanation on here or direction to relevant primary sources is much appreciated.


texts:
Calculating Solar eclipse magnitude with the besselian elements
What is the mathematic formula for calculating the magnitude of a solar eclipse using Besselian elements?


texts: Y dwarf stars have sub-zero temperatures, so I became curious how a star like these dies out and if is could go supernova.


texts:
The Wikipedia article about Europa states

It is estimated that Europa has an outer layer of water around 100 km (62 mi) thick; a part frozen as its crust, and a part as a liquid ocean underneath the ice.

But it doesn't say how thick the icy crust and how thick the liquid ocean is. How many kilometers thick is the crust of frozen water on Europa? Is it roughly the same thickness all across the moon?


texts: Possible to use tachyons to explore black hole?

texts:
I read on a Wikipedia article lately that tachyons are theoretical particles which always travel at or above the speed of light. That means that when one passes us, we see two images, a blue shifted one and a red shifted one.

Black holes on the other hand have gravity so strong that light gets pulled in. However, I haven't heard that black holes can exert a gravitational pull that can pull and object that is travelling greater than the speed of light.

So now, I am wondering that if it is possible to use/make tachyons and control those tachyons, could we send them into a black hole and use them like a "echolocation" thing, except the sensors would be on the other side of where the tachyons are first produced?


texts: How can I find the radius of a exoplanet using doppler spectroscopy

texts:
I have the stellar and planet mass, planet velocity, radial velocity of star, stellar semimajor axis.
How should I go about to find the radius of this exoplanet?


texts: According to the Globe Earth Theory, the Sun is in the middle of the Solar System and the Earth is the 3rd planet from the Sun, making Mercury and Venus between Earth and the Sun. If this is true, Mercury and Venus should only be seen from the lit side of the planet, since it is always between the Sun and Earth. How can you see it at night?


texts:
I decided to try the Astrophotography mode on my phone. Looking at the image I saw an object I didn't notice at the time.
What is the blue circle right of the Moon and just on the top right of the hole between the clouds?

I tried to look at a planetarium (time and location included, no idea about the azimuth). I couldn't find a planet looking at this direction.
According to this (if I understand it correctly) the only planet visible at that time and location should have been Mars.


texts: Where a database of different z values of redshift can be found?

texts: I was working on reshift details for various galaxies but do not know any database to find the z values given to redshift galaxies. Can anyone help?


texts: What will happen if a black hole appears near our solar system?

texts: We know that black hole possesses immense power and can destroy anything coming in front of it's path. If such a black hole appears near our solar system, are we going to survive? Is there any way not to fall in a black hole?


texts: How exactly does inflation convert random gravity fluctuations into coherent gravitational waves?

texts:
In the course of this very enjoyable press announcement, it is mentioned that inflation can create gravity waves by amplifying gravity fluctuations.

I do not properly understand this statement. I always thought that quantum fluctuations (fluctuation of the metric in this case?) should occur pretty randomly whereas waves are rather coherent motions.

So I understand somehow that inflation can amplify quantum fluctuations, but I don't see how it can convert these random "microscopic" processes into "macroscopically" observable coherent phenomena called gravitational waves.
For example, how are the sources of these gravitational waves distributed? Does each point in space-time behave as some kind of a point source? And what is observed at a specific point as the superposition of all these excitations?

In addition, in the same video it is said that not all inflation models produce gravitational waves, the ones that have them are favoured by the data now, etc.


texts:
Many sources indicate that there is ice water on Mars today, but it is mainly traces, here and there, but not that much.

However, solid hypothesis state that there were oceans on Mars, see Wikipedia's Mars ocean hypothesis or at least large aquifers on early Mars. They all concern early Mars so around 3.5 to 4 billions years ago. These theories suggest that Mars oceans could have formed Mesa landscapes (just likeGrand Canyon or Monument Valley).

So my question is simple, if all these hypotheses are true, where did that water go?

Is it possible that so much water could have been evacuated from the planet? I guess it would have needed A LOT of energy.

So it may have been transformed on the planet.

Is it possible that the water has oxidized iron, creating Iron oxide (ie rust) and that it is the main reason for Mars red color?
The Mars ocean hypothesis page suggests some leads about the fate of that ocean, but none suggests the oxidation of iron consuming the entire oceans. Moreover, oxidation would imply the presence of water and dioxygen...

http://en.yibada.com/articles/18182/20150309/red-planet-once-held-large-shallow-ocean-mean-positive-signs.htm


texts:
What is the currently accepted estimated range of the amount of energy of the Big Bang event?

In joules at some estimated size, so a temperature may be calculated.

For context, I wonder if the temperature of the Big Bang would make its heat radiation wavelength shorter than the Planck length.


texts: How were the distances to stars measure before parallax?

texts: A comment under When was the distance to a star measured for the first time without using parallax? mentions that the distance to stars was measured before parallax was possible. How was this done?


texts: In 'Modified gravity' theories like MOND, are galaxies and stars actually, slowly accelerating? In the normal sense? normal

texts:
In M.O.N.D., they say that massive objects, accelerating slowly, experience this modified gravity...
But, are they actually gaining in velocity, albeit very slowly?
Or are the MOND theorists using the term 'acceleration differently, as in the sense that all objects in a gravitational field are 'accelerating', even if they soon end up traveling at a constant velocity?


texts: Would a viewer see Earth from the rim of Shackleton Crater?

texts: I've been researching this but so far have not found an answer.  If you were standing on the top of the rim of Shackleton Crater at the lunar south pole, would you be able to see any of Earth? I can't find anything about the height of the rim, although nearby Malapert Mountain is apparently visible from Earth so you could see Earth from Malapert.  Shackleton, though, I'm not so sure.  Any insights appreciated. KPRedmond


texts: I am doing an Introductory course in astrophysics UG level. I have studied that mass of the gases ($M_{gas}$) decreases with time as new stars are formed but mass of stars ($M_{star}$) doesn't increase because stars die out too. What about the dark matter halo ($M_{halo}$)? Does its mass increase or decrease over time?. Also how do $M_{gas}/M_{halo}$ and $M_{star}/M_{halo}$ change as the galaxy ages?


texts: How did our ancestors discover the Solar System?

texts:
I wonder, how did our ancestors discover the Solar System? They did not have any telescopes to see distant objects, right? Even a planet looks like a star from a distance.

They discovered the rotations of different planets without having much technology.


texts: How thick is the cosmic microwave background, including the part we cannot see within the observable universe?

texts:
What I want to know is how thick the observable universe is from the point of the cosmic microwave background and beyond.

It appears the thickness of the cosmic microwave background itself (the part we can see) is above 100,000 light years, per the following article:
http://scienceblogs.com/startswithabang/2013/06/19/5-facts-you-probably-dont-know-about-the-cosmic-microwave-background/

However, I want to know the thickness of that, plus what lies beyond that we cannot see, another way of looking at it would be the distance between the surface of last scattering (cosmic microwave background end) to the beginning (e.g. Big Bang).

According to the following article, it appears that this time from the beginning to the surface of last scattering is about 300,000 years:
https://ned.ipac.caltech.edu/level5/Glossary/Essay_lss.html

That would imply that the thickness should be about 300,000 light years, but that doesn't take inflation into account.

What is the thickness (in the observable universe) between the beginning (e.g. Big Bang) to the surface of last scattering (Cosmic Microwave Background), including inflation?


texts: What is the next planned mission that can discover life on another planet?

texts: I've heard that we have a great shot at finding life on Mars if we just drill deep enough down to the surface to the water and detect if its sterile or not. Are there planned missions to do this? If not, what is the next (or existing) mission where finding life is likely? Is it launching something to Mars, Europa, Titan, or some other moon? Why does the mission have a good shot at finding life?


texts: When black holes forms out of a supernova do they have a very high velocity?

texts: When black holes forms out of a supernova do they have a very high velocity ?? Or do they remains at the position of parent star ??


texts:
I'm watching this YouTube video, and in it, the lecturer explains a model of planetary orbit. At 1:55 he shows how a marble will naturally orbit the center object, and he briefly claims that planets will not lose energy like the marble does. But I cant see how that is the case. Surely there must be meteors, asteroids, comets, including general space debris, that will over the course of millennia, diminish this energy/momentum.

How then, can planets retain their energy, when there are almost only forces that would slow it down? Slowly increasing the energy wouldn't help either, as it would offset the balance. How can there be stability, especially over the course of millions of years?


texts:
In doing research on vision, I have learned that "20/20" vision corresponds to a visual acuity of being able to resolve details 1 arcminute in size, that most people have around 20/15 vision, and that due to the limits of physiology basically nobody has vision better than 20/10 vision. This is an upper limit of resolving details about 0.5 arcminutes in size.

According to Wikipedia the moon is around 30 arcminutes wide when seen by the naked eye.

Put these together, and it seems to say that when looking at the moon with the naked eye nobody can see more details than would be visible in a 60×60 image of the moon

and that the average person can't see any more details than in a 40×40 version

Those seem so small on my monitor. Can that really be all the detail that I can see on the moon with the naked eye?


texts: Determine distance from the galactic center in DS9

texts:
I have a list of coordinates of black hole/neutron star systems in decimal degrees (ie. {(266.416,-29.009), (266.418,-29.009),...} from DS9 and would like to determine the distance from SgrA* in parsecs. To my knowledge, 25.8 parsecs ~ 1 degree, but the distance I calculate do not agree with values previously determined by a colleague.

For example, I have a list of nine very faint X-ray transients (VFXTs) and their coordinates, one of which is (266.4191667, -29.0101111). Using the distance formula, I estimated the degree distance from SgrA* - from Wikipedia, in decimal degrees, (266.4168371,-29.0078106) using the Euclidean distance formula and multiplied my value to get

  (25.8 pc/deg)(0.00327404 deg) = 0.0844702 pc

from the center; but this value does not agree with any previously determined values of the VFXTs offsets.

The list I received from my colleague for VFXT offsets is

"vfxt_d = [.7209, .8605, 1.0233, 3.1395, 3.1628, 10.4651, 14.8372, 25.6744, 29.2093] "

I would appreciate some pointers to complete this project sometime today. Thanks in advance.


texts: What's the most distant object we've measured by parallax?

texts:
The openstax Astronomy textbook says that when the Gaia mission is complete, we'll have parallax measurements to 30k light years. Do we have those now?

What's the most distant object astronomers have measured by parallax so far?


texts: What is the length of time for each fusion process in a massive star?

texts: In a massive star (i.e. an O5 star), first hydrogen is fused into helium, then helium is fused into carbon. This process continues to neon, oxygen, and finally silicon burning. So I am wondering, how long does it take for each process to commence?


texts: Is it possible to throw a camera attached to a rope within the event-horizon of a black hole and then pull it back in?

texts: I have heard that when something passes the event-horizon of a black hole nothing can stop it from getting pulled in. Is that true for objects partially past the event-horizon? Would it be possible to attach a camera to a stick or rope, put it inside the event-horizon, take a picture, and pull it back up and look at the picture?


texts: Does gravity bend light, and how much time does it take for light to cross gravity of a Black Hole?

texts:
This is very confusing to me, so the question might be same. Please go through it, if required i will add more text.

According to Einstein's theory of general relativity, photons are not technically affected by large gravitational fields; instead space and time become distorted around massive objects and the light simply follows this distorted curvature of space.

My questions are:
1) For example: 1 hour near a black hole, is equivalent to 100 Years on Earth. If the light travels through this distorted space and time around a black hole, how much earth time does it take for light to cross the black hole's gravity?

2) We say the Universe is 14 Billion Years old, and its diameter is 91 Billion Light Years approximatly. My assumption is, these age and diameter of universe is based on the measurement of the light travel (Light is one of the factor in many).

3) So, if first (1) and second (2) points are right, how can we say the Universe is created 14 Billion Years ago (if light takes 100 Earth Years to cross over the black hole's gravity)?


texts: Calculate the shadow on earth of a large orbital disk

texts: How to calculate the shadow on earth of a large orbital disk (low orbit)?


texts: Do astronomers, in principle, have more information about older phenomena than younger?

texts:
The further away we see, the older states of the world we observe. And the volume of the part of space which is observable, increases by the square of the distance to it. So there should basically be a million times more phenomena (data) observable about what happened a billion years ago, than about what happened a million years ago. Given good enough observatories.

This is obviously counter intuitive, and sorting it out for so called redshift effects doesn't help in that respect. Do/can we really (potentially) know more about things/events the older they are? Is there some epistemological problem involved in that?


texts: Why can't neutron stars ignite and explode?

texts:
Beyond the Chandrasekhar limit, white dwarfs become extremely hot. As a result, previously unfusable carbon can become fusable, causing nuclear reactions. This leads to a thermal runaway and ultimately a type Ia supernova.
However, this doesn't seem to happen in neutron stars. They can keep gaining mass until they become black holes. After a certain point, shouldn't the immense temperatures cause a thermal runaway like in white dwarfs, leading to their explosion?


texts: The moon was first formed billions of years ago when a Mars-sized object crashed into Earth. The pieces formed over time to create our moon. Why was only one moon formed? Could Earth have had other moons that no longer exist?


texts: Why doesn't this paradox disprove (some) multiverse quantum gravitational theories?

texts:
As I understand it, one theory of the multiverse is that there are an infinite number of universes separated by small distances in other (than our observable 3/4) dimensions and that gravity is weak because it permeates these other dimensions.

But if there are an infinite number of these universes then surely the gravitational force we would feel would be infinite?


texts: How to isolate H$_\alpha$ from Nitrogen doublet emission lines

texts:
I am trying to find out line intensity and FWHM of H$_\alpha$6565 emission line from a quasar spectrum obtained from SDSS DR-14Q. Visual inspection of spectrum shows H$_\alpha$ being contaminated with [NII] 6549,6585 emission lines. I tried fitting voigt profile on the emission line to extract FWHM and line intensities. But the problem is voigt profile is not being fitted properly onto the data as shown here
I tried fitting 3 gaussian profiles on the data as there are 3 peaks visible. While fitting multiple gaussians it is clear that the gaussian profile doesn't fit over the left and right wings of the data.

I have already subtracted the underlying continuum and tried to normalize the flux as well.
Can anyone comment if I am doing it correctly because in both cases it seems that there is some sort of data loss? Or can anyone suggest a better way to do that?


texts:
A few days ago (september 2020) a planet candidate was announced orbiting white dwarf WD 1856+534. Some media outlets announce it as the First Possible ‘Survivor’ Planet around a white dwarf, while others even say it is the first planet around a white dwarf. Some add that if further confirmed, (...) shows that some planets could survive the destruction of their sun-like stars. I can't find the source, but I even recall reading an article saying that the host being a stellar remnant was what made this finding relevant.
However:

the first confirmed exoplanets (1992) orbit a stellar remnant (PSR B1257+12),
there are other planet candidates around white dwarfs, and
it is not confirmed that the planet survived the death of its host star (as opposed to being formed or captured later).

Another highlight given is that it is still to be explained how such a planet survives being so close to its star, but do we know the planet is beyond its Roche limit?
I am puzzled: what exactly makes this planet's finding so special/a first? Is it just de degree of certainty about one of the previous assertions? (First around a WD, first survivor.) Is it something else? Or was it just a case of recency bias that made the discovery more visible?


texts: Normalizing the supernova spectrum by photometry

texts:
I have a SN spectrum here (already reduced) that seems to have some artifacts. Professor tells me that I may have to normalize it using photometry.
As far as I understand, I just have to multiply it by some factor to make the integral over all frequencies equal to bolometric luminosity. Am I right, or is there some more complicated thing here?


texts: Hubble law, cosmological redshift and distance

texts:
I have got confused with some cosmology formulas which calculate distance.

The most famous formula is indeed the Hubble law which says (nowadays) velocity is proportional to Hubble's parameter at current time.
On the other hand we can find the velocity from redshift.

By Hubble law it is possible to evaluate distance but it's not clear for me that what does this distance mean...! As the photons, which are now observed, are belong to another redshift (larger) and by traveling toward Earth the have become "redder" because of expansion of universe, what does the observed redshift stand for?
The actual redshift of the galaxy at observation time (although we can't recieve the photons now), the redshift at emission time (that means we do not calculate current distance of the galaxy) or something else?

Thanks a lot.


texts:
I have a flux value in the infrared band of 8 mJy at a wavelength of 80 microns that I want to translate into X-ray conventional flux of keV/cm^2/s/keV.
I have tried many conversion factors but none of them is helpful (see e.g. https://hea-www.harvard.edu/~pgreen/figs/Conversions.pdf). This table for example gives a conversion factor of $10^{-26}$ from mJy to erg/cm^2/s/Hz, and this is correct. However, when I go from erg/cm^2/s/Hz to keV/cm^2/s/keV, an additional $10^{26}$ factor comes out from the transformation of ergs and Hz. This cancels out with the previous factor and an unbelievable IR flux results, higher than the actually measured X-ray flux.

I know that the IR flux is much less than the X-ray flux, but can not find an appropriate way to convert.


texts: Last night I was randomly surfing astronomy pages and came across this.I searched up Wikipedia and other sites,but it doesn't exactly give me enough information about their characteristics.


texts: Is it conceivable that the presence of chlorophyll (or similar) could be distinguishable from other chemicals on an exoplanet?

texts:
If an Earth-like exoplanet had a sufficiently extensive plant biosphere (i.e large forests, aquatic algal mats etc), is it at all conceivable that scientists could spectroscopically detect the presence of biochemicals, such as chlorophyll, anthocyanins etc?

If possible, how would the spectra of these biochemicals be distinguished from other chemicals?


texts: At what distance would it be safe for humans to stare at the sun?

texts:
Let's say we could travel anywhere in the solar system, at what distance would it be safe for a human to stare at the sun (without eye protection) and not get eye/retina damage?

(Not sure where this question is good for, here, or perhaps Biology.SE, so let me know.)


texts: Was this an astronomical phenomenon observed in 1689?

texts:
In a Swedish church record from 1689 a phenomenon in the sky is described. With my very limited understanding it could be a meteorological or an astronomical phenomenon, so here I ask if it could have have an astronomical phenomenon, and what it was in that case.
The place
The observations were made from the village of Fagerhult in Kalmar län in Sweden, at 57°08′55″N 15°39′52″E, in the sky to the North-East.
The time
This was 18 December 1689 (according to the Gregorian calendar – actual date given in the document is Julian 8 December).
It was "around 4 in the afternoon, around sunset". (I think that sunset actually was at about 3:15 PM local time.)
Description
It is described as an elongated cross with the long arm being about 6 times as long as the short arm. I think it means to say that the long arm was vertical, but I'm not sure about that. The cross was shining clearly on the sky, a burning light in the north-east for about an hour. It was almost a clear sky and where the cross was there were no clouds at all.
The account is accompanied by this illustration. It doesn't have the same proportions as I understand the text to say. Maybe the image is better than the text.

(Undoubtely this led to religious ponderings, and that was presumably why this was recorded, but there is actually nothing of that in the note – just this description.)
Was there anything special happening in the sky then that could have to do with this?


texts: How and when did we learn about the universe?

texts: I'm 13 - I'd like to know how we found/discovered important details about the Universe. I know we have found many different things about the Universe, but when did we find how amazingly large the Universe is?


texts: Does the ecliptic precess? Does the Sun's rotation precess?

texts: We know that the Earth, like a top, slowly precesses as it rotates. We know the Sun rotates, but does it precess as well? What about planetary orbits? Is the orientation of the ecliptic stable or will its inclination change over time? If so, would the orbital inclinations of the planets currently in the ecliptic change independently or in unison? We know the ecliptic is inclined with respect to the galactic plane. Would that have been a consequence of "residual" angular momentum when the solar system formed, or did it gradually take up its present orientation?


texts: How can only 1 magnetic pole of the Sun change at a time?

texts: I read some news stories about the current Solar maximum and the flipping of the magnetic poles. They say that one of the magnetic poles has switched polarity and the other will switch in about a month. I don't really understand magnetism, but I had thought you had to have 2 opposite polarity magnetic poles. How can the Sun's magnetic poles not switch in sync with each other?


texts: Why the habitable zone of a binary star is a disc and not a sphere?

texts:
I understand that the orbit of a planet will always be flat, so there is no point on making a sphere out of the HZ when we consider one star, but what about binary stars? For example, this binary system (taken from here):

The habitable zone of this binary surrounds both stars, but what if the orbit of the planet isn't contained in the binary's orbit plane? For example, orbiting the star on the left with an inclination of, say, 20 degrees? Wouldn't it have to be two spheres and not two disks? Or is the HZ calculated assuming coplanar orbits?


texts: Does all the exoplanets orbit the same direction?

texts: In one stellar system like our milkyway, all the planets orbits in the same direction. But are exoplanets orbitting in the same direction as we (earth) do, or is there a higher percentage which orbit in one or the other way? If so what could be the reason for that?


texts: Where can I find Helium 3 in our solar system?

texts: What are the best locations within the solar system to find Helium 3 excluding the Sun? Where is Helium 3 most abundant after the Sun?


texts: Could the Sun's bending of light be measured on photographic plates before Einstein's prediction?

texts: It was predicted from Newtonian physics already in the 18th century that gravity should bend light, but not by as much as general relativity predicts. This was first confirmed during a solar eclipse in 1919. Surely, solar eclipses were imaged long before that. Didn't anyone notice that stars near the Sun were displaced? Hadn't anyone thought of testing the newtonian prediction of bent light?


texts: Getting Solar Noon from Sunset and Sunrise

texts:
I've seen the solar noon formula described as snoon = 720 – 4*longitude – eqtime. I'm curious if it is equally reliable within a relatively small margin of error (+-60 seconds) to simply get the midpoint between sunrise and sunset, given that data is already calculated and available.

Is there any occasion when solar noon wouldn't be equal time from sunrise and sunset, give or take the aforementioned margin of error?


texts: What types of star do we know are hostile to life (like ours)?

texts:
Certainly all stars have enough energy for a planet to host life. But a more magnetically active star is not preferred because solar ejection could strip planets of their atmosphere. What's the right balance?

Which stellar category of a star is suitable for hosting life excluding G2V class (our Sun's category)?


texts: What percent of all stars that have lived (up to now) are stellar remnants?

texts: According to this post, I found that about 90% of all stars are main sequence stars. So I am assuming that the other 10% consists of protostars, older giant stars, and stellar remnants. So I'm wondering how much of the stellar population is dead (i.e. turned into a remnant, excluding supernova progenitors that blow apart the whole star without leaving anything behind)?


texts: How active was the Milky Way in its first 5 billion years?

texts: When I look into the history of the Milky Way, it seems like the Milky Way has been the pinnacle of stability. It seems highly likely that our galaxy has eaten several smaller galaxies/dwarf galaxies in the past. Also, our galaxy seems to be one of the first to form. I am wondering if our seeming stability is the result of our galaxy's age. So, was the Milky Way more active (as far as stellar formation, supernovae, etc.) in its early years? How do we/ could we know?


texts: What are the reasons for referring to equinox J2000 or the equinox of the date?

texts:
(Background: Trying to learn something about the mathematical and computational part of astronomy I have acquired a copy of Meeus' "Astronomical Algorithms" and implemented the material up to Chapter 33 in Java, with only one major sidestep: VSOP87, for which I obtained the full data set and "translated" the FORTRAN program.)

VSOP87 exhibits the reason for my question: you can compute rectangular/spherical heliocentric positions either for the reference frame J2000 or the one of the given date. Clearly, if I want to observe some planets tonight, I'll compute the data for today's equinox. On the other hand, there is the possibility of a transformation between equinoxes of different dates.

So why are these methods (here and for other methods, too) provided for both reference frames? Was it the (then) weaker computer performance?

Only a little later, iauPlan94 provides the result only for J2000 although Meeus in the chapter dedicated to the paper of J.L.Simon e.al. provides tables with data from their theory for J2000 and the equinox of the date.

What would be good reasons for today and the years to come to refer a computation to J2000?


texts: How String Theory calculates the Entropy of the Black Hole in a Background dependent way?

texts:
How does string theory get an agreement to the Hawking-Bekenstein equations to calculate the quantum entropy of a black hole in a background dependent way?
Is there any sort of area parameter in string theory like Barbero-Immirzi in loop quantum gravity?


texts: Is there an example of a star that is already dead, but can still be seen on Earth?

texts:
While looking up at the stars I wondered, what are the odds that some of them are already dead. I did some research and found a very interesting article here. It states that the odds are rather small, so it is not like about 50% of the stars we see are already dead.

But I still wonder if there is an example of a star we know to be already gone, while it is still visible on earth.

As far as I know, the only way to find out is to watch the stars light. So if the light "goes out", we know the star has been gone for quite some time. Assuming this to be fact, I would have to conclude that such an example does not (and cannot) exist.

Is this true? Or is there in fact a star that is already dead that we know of, which can be seen in the sky?

PS: By "seeing the star" I am talking about a star that looks just like any other star in the night sky (not, for instance, a visible supernova).

Edit: If there is such a star, how did we find out it is already gone?


texts: What is the area of the Summer Triangle?

texts:
I'm pretty sure spherical trigonometry comes into use here but I don't know how to calculate the area. I'm pretty sure Vega, Deneb, and Altair's declination and right ascension figures need to be converted to coordinates, but again, I have no idea how.
Is there a formula for a general case like this? Not necessarily just the Summer Triangle, but a formula for the area enclosed by any 3 (or more) stars on the celestial sphere?


texts: Why you use log to measure metallicity in galaxies?

texts:
For example, I saw the next expression for matallicity in a paper: $\log(O/H) + 12$.

I understand O/H is the O(Oxygen) to H(Hydrogen) ratio but why is there the number 12? And why the logarithm?


texts: Does the recent news of "ten times more galaxies" imply that there is correspondingly less dark matter?

texts:
Nature: Universe has ten times more galaxies than researchers thought

NASA feature: Hubble Reveals Observable Universe Contains 10 Times More Galaxies Than Previously Thought

Headlines sometimes oversimplify. But if this is really true, that there seems to be about ten times more galaxies than had been generally assumed, does this impact other assumptions? Does this imply the universe is ten times more massive, or just that there is less dark matter than was previously thought.


texts: If an Asteroid, the size of the one that killed off the dinosaurs , passed by very close to the Earth but still remained outside of Earth's atmosphere, would it cause any damage ?


texts: Conventional matter to dark matter ratio, outside of galaxies

texts:
Consider say this outstanding diagram from another question,

To begin with galaxies have a typical density D. Intergalactic space has a much lower density d.

As we know: in galaxies (with density D) most of the stuff is dark matter.  Let's say for convenience it is 10:1.

So, the ratio of dark matter in galaxies is (we'll say) 10:1.

But here's what I can not find explained anywhere:

(1) In intergalactic space. First of all simply is there any dark matter?  Or, do we believe that dark matter exists, simply, only in galaxies? Not between?

(2) If there is dark matter between galaxies. Do we know or believe: what is the ratio of dark matter out there?  In fact, is it just the same ratio (say, 10:1) as inside galaxies? Or, is it perhaps even more dominant, or perhaps much less dominant?  What is the ratio out there?

(3) If there is dark matter everywhere. Galaxies exist in filaments and walls.  Does dark matter do this? or is it evenly-spread?


texts:
In a paper I've read, I have seen the following:

In view of the noise levels, it is difficult to perform such a search effectively using statistical significance criteria only. We will therefore appeal to spectroscopic consistency arguments when assessing apparent absorption features in the spectrum. As a guide, however, we estimated the significance of the features by fitting each with a simple gaussian profile, optimizing the continuum, and evaluating their significance in terms of the amplitude of the gaussian. In the early-phase spectrum, the depth of the 13.0 Å  feature differs by 7 sigma from zero, whereas those of the 25.3, 26.3 and 26.9 Å features differ by 3–4 sigma.

What does "the depth of the 13.0 Å  feature differs by 7 sigma from zero" mean?
How these  significance level calculate? The line seems weak and could not fit with normal fitting method. So use chi-squared method seems do not work.
And another way to calculate such weak line significance level is to use equivalent width divide the uncertainty, but to the so narrow absorption line, how to calculate or get the uncertainty of the equivalent width?


texts: Retrograde motion and Kuiper Belt Objects

texts:
As seen from Earth, planets such as Mars and Jupiter exhibit retrograde motion when they are near opposition (from Earth).  I am wondering how this effect extends to very distant objects, such as those in the Kuiper Belt.

Since objects in the Kuiper Belt orbit the Sun at a velocity much slower than Earth (or Mars or Jupiter for that matter) because of Kepler's third law I'd imagine that retrograde motion for these objects is more extreme in the sense that these objects are seen to be in retrograde motion for a longer time and over a larger portion of the sky (in an angular sense) than would be seen for any of the planets.

In an extreme case, is it possible that a very distant Kuper Belt Object (KBO) would never be observed in prograde motion?  I imagine that if you were to observe a KBO that was in the direction of Earth's motion then there would be no contribution from the Earth's velocity on the observation and you would be able to see the object in prograde motion, no matter how slow it was travelling. However, such an object would likely be obscured by sunlight, since objects that lie in the direction of Earth's motion lie above the day/night interface on the Earth.  My question here is that, given real-life observational constraints (like sunlight) how far from the Sun would an object have to be to never be seen in prograde motion?  You can be mathematical.


texts: Do we know of any tidally-locked planets with atmospheres?

texts:
If not, is there any reason such a planet couldn't exist?

I ask only because that planet would literally have a twilight zone and I want to know that that's a thing somewhere.


texts: How to calculate local position, knowing the RA and Dec of the center of an image, RPY of the camera, and precise time?

texts:
Given a picture of stars - assume it is possible to identify the stars and their Right Ascension (RA) and Declination (Dec).  By choosing one near the center of the image (or interpolating RA/Dec to the center) the effective "pointing angle" of the camera would be known.

With the RA/Dec of the camera, plus the Roll (R), Pitch (P), and Yaw (Y) of the camera, and the precise time (TAI, UTC, and/or UT1) the picture was taken... how would a location calculation of where the camera was on Earth when it was taken be possible (assume it is possible).

It seems like it would be a simple coordinate transformation, however understanding how time affects the calculation isn't clear.  I can't find a simple resource of algorithms to find one close enough.

ETA: Roll, Pitch, and Yaw could be found in a few different ways... in my current case I took a good first initial "guess" and then plotted an overlay of stars based on perturbing the initial first guess until the stars overlaid well over the image (of course, this required I knew where the picture was taken!)  However, it is also possible to know R,P,Y based on a local gravity vector and inertial mechanics (a simply INU)... which is where I would eventually like to get to.

The RA and Dec is currently found using http://astrometry.net/ by uploading the picture they returned astrometric meda-data.

Here is an example set of numbers:
R=10.7deg, P=63.1deg, Y=-174.8deg

Time=2016,Oct,1,0hr,31m,28s

Leap Secs=36 GPS-TAI

UT1-UTC = -0.28

Center of Image (~pointing vector of camera)

RA = 90.7 (6h,2m,53.422s),

Dec=3.56(3deg, 33' 24.95)


texts: Do solstices and equinoxes shift over time?

texts:
Right now, I think the winter solstice is around December 21. Has it always been around this date constantly?

Since the earth's axis's 23.45° tilt will be on the exact opposite side in 13000 years (or was 13000 years ago) due to precession, it'd seem like the seasons would flip every 13000 years. So, +/- 13000 years from now, it would've turned summer around December 21 in the Northern Hemisphere, right?


texts: If there were an asteroid orbiting its star within the habitable zone and this asteroid contained liquid water, would it be possible for simple life such as bacteria to form?


texts: Roche Zone of a black hole vs Roche Zone of Neutron Star

texts:
Suppose a very unusually small back hole with the mass of about, lets say, 1.5 solar masses(hawking radiation should destroy a lot of mass let's assume). It thus would have a Roche limit smaller than larger black holes, and the Roche limit should be outside of the black hole instead of inside it, like some supermassive black holes.

Then, let's take a super massive neutron star, perhaps even with quark matter at its center. Even though this may not exist, let's say that is 3 solar masses by taking matter from a nearby red giant rather slowly. This would mean that it thus has a larger Roche limit.

Then, let's fit the two together in a binary system. Move the black hole inwards so that it is in the Roche limit of the neutron star, but its Roche limit is not affecting the neutron star.

My question is that, since a black hole can't physically be ripped apart by gravity due to it being a hole in space time itself, can it's structure be altered in any way by the gravitational pull of the neutron star? Like from a sphere to an oval or something like that? Can it separate into two smaller ones due to the gravity of the neutron star? In the system, who would win the gravity war?

Now assume that the black hole has angular momentum and change, giving it a magnetic field. Then make the neutron star a magnetar of the strongest kind, and place them in the same binary position as I described above. Would their magnetic fields have an effect on any of the bodies that are generating them? Would their magnetic fields have any effect on the other object's magnetic field?


texts: Observing the night sky with a 6-year old

texts:
We currently possess a Celestron NexStar 130 SLT computerized reflector telescope and have an opportunity to do backyard astronomy with my 6-year old daughter from time to time.

She is quite interested in space and astronomy, knows a lot of objects in the Solar System, which have atmosphere and what don't, knows major planet satellites and thinks there is life on Titan.

But, I find it quite challenging to actually do telescope observations with her:

it takes time to set things up, assemble the equipment and align the telescope. She is not patient enough and that sometimes "kills" all the fun and excitement
it is not easy for her to get used to looking through an eyepiece
it is easy to touch the telescope which leads to a shaking image

What are the general guidelines to observe the night sky with the 6-year old? What can I do to make the process less tedious, more fun and engaging?

(we also have the 15x70 Binoculars)


texts: How deep is the "A" Fraunhofer line in the solar spectrum? Is it from the Sun's or Earth's atmosphere?

texts:
Question: Where can I see - or even download - a fairly high resolution (~0.1 nm) solar spectrum at zero air mass - in other words from space without absorption and other features from the Earth's atmosphere? Of particular interest is the near infrared around 750-780nm. Is the "A" Fraunhofer line due to absorption by oxygen in the Sun's atmosphere, or in Earth's?

The background discussion below shows some examples, but these are not directly from scientific sources and I have a hunch they are from observations on Earth's surface below the atmosphere.

Background:

Studies of photosynthesis on Earth using spectrometers in satellites measure solar flux induced fluorescence from foliage during the day, taking advantage of certain bands in the solar spectrum that are relatively "dark". GOME-2

For example, the Fraunhofer line labeled "A" below is produced by absorption by oxygen, but it is not clear to me if it is the oxygen in the Suns atmosphere or the Earth's atmosphere that's producing this line.

The images below are spectra of sunlight with various instruments of widely different resolutions, and because the absorption is narrow, the apparent depth is a function of resolution rather than reality.

above: a low resolution spectrum from here

above: An spectrogram of the Sun from this NOAO website (N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF) with the "A" line near 760nm appearing near the top, a little right of center. The original data is from the "Fourier Transform Spectrometer at the McMath-Pierce Solar Facility at the National Solar Observatory on Kitt Peak, near Tucson, Arizona" but seems to be formatted and colorized to look like an Echelle spectrogram.

A video describing the use of the dark band for Earth science can be seen at https://youtu.be/1XilneV3cJI.


texts: Are there any bright non-stellar objects which make up asterisms?

texts:
Hopefully the title is very self-explanatory. I was wondering if there were any non-stellar objects, such as bright galaxies, which when looking with the naked eye were mistaken for stars in the time when asterisms were documented and catalogued...

For example, within the Big Dipper I believe it is Mizar which is in fact a binary star system. (Correct me if I am wrong!)

I was hoping perhaps for distant yet bright Messier objects being mistaken for stars...